This invention relates to a method of testing joints formed by bonding of tubulars and to an apparatus for carrying out such method.
Conventionally, tubulars used in the construction, maintenance and repair of oil and gas wells are joined by mechanical couplings. Typically, one tubular is provided with a threaded socket which receives a threaded pin on the next tubular. The mechanical characteristics of the couplings are well known and although it is not unusual to test the joints to make sure they are not leaking it is not customary to check them for their load bearing ability.
While mechanical couplings are quite adequate for many situations, they do have certain disadvantages. In particular, they are prone to failure in wells which contain highly corrosive vapors. In such wells it is not uncommon for the entire string to have to be replaced every few years. However, in the absence of such mechanical couplings it is widely believed that the tubular itself could be expected to have a working life of about 25 years.
Welding has been attempted as an alternative to mechanical couplings. However, this is difficult to carry out in the hazardous environment present at the top of an oil or gas well. Furthermore, normal welding generally creates metallurgical discontinuities which provide areas which are also susceptible to corrosion.
Amorphous bonding is a technique which has been successfully used for joining metal parts, particularly in the automotive industry, for several years. In general terms the surfaces to be connected are ground until they are exactly parallel. Next a thin film of a special alloy is placed between the surfaces. The pieces are then pressed towards one another and heat applied for several minutes. This process results in a finished component which has a nearly homogeneous metallurgical structure. It will be appreciated that it would be highly desirable to use amorphous bonding for the connection of tubulars for use in oil wells.
It is known from U.S. Pat. No. 2,761,310 to use a device for fatigue testing a welded tube, wherein the tube is heated and pressurized and one end of the tube is rotated so that the tube is twisted in opposite directions. U.S. Pat. No. 3,845,657 discloses the use of strain gages for detecting cracks in the welds of pipes.
The present invention is concerned with an improved technique for testing the joint after it has been made by an amorphous or other bonding process. The technique could also be used for testing joints made by other bonding processes than amorphous bonding, for example by welding or by adhesive.
According to the present invention there is provided a method of testing a joint formed by bonding of two tubulars, which method comprises the steps of:
a) providing a first tubular and a second tubular, wherein an end of the first tubular is bonded to an end of the second tubular to form a joint therein between;
b) holding said first tubular;
c) applying a force to displace said second tubular relative to said first tubular;
d) removing said force; and
e) comparing the final position of said second tubular with the position which it occupied prior to step (c) by means of a sensor mounted remote from said joint.
The present invention also provides an apparatus for testing a joint formed by bonding of two tubulars which apparatus comprises:
a) a fixing device to hold a first tubular;
b) a head to grip a second tubular, an end of second tubular connected to an end of said first tubular to form a joint;
c) a sensor remote to said joint, which sensor is responsive to the position of said second tubular;
d) means to move said head to displace said second tubular relative to said first tubular; and
e) means to allow said head to move to a position dictated by said second tubular.